Elementary chemistry
External link: Periodic table at ptable.com An atom is the smallest constituent unit of ordinary that has the properties of a . Every , , , and is composed of neutral or atoms. Atoms are extremely small; typical sizes are around 100 s (a ten-billionth of a meter, in the ). Componests Every atom is composed of a and one or more s bound to the nucleus. The nucleus is made of one or more s and typically a similar number of s. Protons and neutrons are called s. More than 99.94% of an atom's is in the nucleus. The protons have a positive , the electrons have a negative electric charge, and the neutrons have no electric charge. If the number of protons and electrons are equal, that atom is electrically neutral. If an atom has more or fewer electrons than protons, then it has an overall negative or positive charge, respectively, and it is called an . The electrons of an atom are attracted to the protons in an atomic nucleus by this . The protons and neutrons in the nucleus are attracted to each other by a different force, the , which is usually stronger than the electromagnetic force repelling the positively charged protons from one another. The electron is by far the least massive of these particles. Under ordinary conditions, electrons are bound to the positively charged nucleus by the attraction created from opposite electric charges. Protons have a mass 1,836 times that of the electron. The number of protons in an atom is called its . Neutrons have a free mass of 1,839 times the mass of the electron. Bohr model In 1913 the physicist proposed a model in which the electrons of an atom were assumed to orbit the nucleus but could only do so in a finite set of orbits, and could jump between these orbits only in discrete changes of energy corresponding to absorption or radiation of a photon. This quantization was used to explain why the electrons orbits are stable (given that normally, charges in acceleration, including circular motion, lose kinetic energy which is emitted as electromagnetic radiation, see ) and why elements absorb and emit electromagnetic radiation in discrete spectra. Later in the same year provided additional experimental evidence in favor of . These results refined 's and 's model, which proposed that the atom contains in its a number of positive s that is equal to its (atomic) number in the periodic table. Until these experiments, was not known to be a physical and experimental quantity. That it is equal to the atomic nuclear charge remains the accepted atomic model today. Valence Valency is the combining power of an element. It is equal to number of hydrogen atoms that atom can combine or displace in forming compounds. The outermost electron shell of an atom in its uncombined state is known as the , and the electrons in that shell are called s. The number of valence electrons determines the behavior with other atoms. Atoms tend to with each other in a manner that fills (or empties) their outer valence shells. :For example, a transfer of a single electron between atoms is a useful approximation for bonds that form between atoms with one-electron more than a filled shell, and others that are one-electron short of a full shell, such as occurs in the compound and other chemical ionic salts. However, many elements display multiple valences, or tendencies to share differing numbers of electrons in different compounds. The s are often displayed in a that is laid out to display recurring chemical properties, and elements with the same number of valence electrons form a group that is aligned in the same column of the table. (The horizontal rows correspond to the filling of a quantum shell of electrons.) The elements at the far right of the table have their outer shell completely filled with electrons, which results in chemically inert elements known as the es. Elements A red circle is an unpaired electron in the outermost shell. A blue circle is a of electrons. Each electron shell is twice the radius of the previous shell. Copper is whats known as a . Zinc has a very low boiling point. |} Silver is whats known as a . Cadmium has a very low boiling point. |} Gold is whats known as a . Mercury has a very low boiling point. |} |} Note: The metallic forms of the elements have electronic structures that differ slightly from the one the predicts. Molecules Each unpaired electron in the outermost shell (called the valence shell) forms a with an unpaired electron in the outermost shell of a neighboring atom. Pure gas consists of . : (H2), (F2), (Cl2), (Br2), and (I2) all form . So does (N2) and (O2). Atoms that have no unpaired electrons in their valence shell are called . Noble gases do not form chemical bonds and are therefore . (He), (Ne), (Ar), (Kr), (Xe), and (Rn) are noble gases. : A single molecule of consists of one Fluorine atom and one hydrogen atom and is therefore diatomic. Fluorine is a powerful . In fact, Fluorine is the most element known. (It really likes electrons). Fluorine is much more electronegative than hydrogen. This causes Hydrogen Fluoride to be a . :: A single molecule of (H2O) consists of one oxygen atom and two hydrogen atoms. Water is a polar molecule. :: A single molecule of (NH3) consists of one nitrogen atom and three hydrogen atoms. Ammonia is a polar molecule. :: A single molecule of (CH4) consists of one carbon atom and four hydrogen atoms. Methane is a hydrocarbon. Hydrocarbons are non-polar molecules and therefore not soluble in water. Methane is a gas. It boils at -161 °C. :: A single molecule of (C2H6) consists of two carbon atoms and six hydrogen atoms. Ethane is a gas. It boils at -88 °C. :: A single molecule of (C2H6O), also known as drinking alcohol, consists of two carbon atoms, six hydrogen atoms, and one oxygen atom. . :: A single molecule of (C8H18) consists of eight carbon atoms and eighteen hydrogen atoms. Octane is a liquid. It boils at 125 °C. If the chain were even longer and the hydrogen atoms were replaced with fluorine atoms then you would have . :: But Benzene is a little bit different. A single molecule of consists of six carbon atoms and six hydrogen atoms arranged in a ring. Each carbon atom bonds with 2 other carbon atoms and with one hydrogen atom thus accounting for three unpaired electrons per carbon atom. But, as we already know, each carbon atom has four unpaired electrons so one electron per carbon atom is unaccounted for. There are six carbon atoms therefore a total of six electrons per benzene molecule are unaccounted for. Those six form the blue circle around the molecule. See also: , , and . Benzene molecules are shaped like flat plates. (See .) :: A single molecule of consists of five carbon atoms, five hydrogen atoms, and one nitrogen atom arranged in a ring. Six unpaired electrons form the blue ring around the molecule. Pyridine is a nitrogen . :: consists of carbon atoms densely packed in a regular hexagonal pattern: :: consist of a two-dimensional hexagonal lattice of carbon atoms, bent and joined in one direction so as to form a hollow cylinder: :: A single molecule of is a of carbon atoms: :: Acids and Bases is a : :: :Its Boron atom has a vacant orbital which can form a covalent bond by sharing a lone pair of electrons on an atom in a base (in this case ammonia).Wikipedia:Acid See . :: A molecule of consists of one Antimony atom and five Fluorine atoms. :: :Its Antimony atom has a vacant orbital which can form a covalent bond by sharing a lone pair of electrons with a sixth Fluorine atom (actually its an ion) thus creating Antimony hexafluoride. :: Note that the molecule in the image above has a net negative charge of -1. I would guess that the reason the six pairs of electrons are able to share the outer electron shell in antimony is because of sd5 . Antimony hexafluoride form a with ions creating which is the strongest known with =-28. :Thats 1016 times stronger than 100% which has H0=-12. It has been shown to even hydrocarbons (which cannot normally be "protonated"). It can only be stored in containers lined with Teflon. From Wikipedia:Grotthuss mechanism: Proton jumping is the process by which an 'excess' proton diffuses through the network of water molecules or other hydrogen-bonded liquids through the formation and concomitant cleavage of covalent bonds involving neighboring molecules. The details of the hopping and transport mechanism are still debated. References Category:Elementary chemistry